Transcript for When you eat matters as much as what you eat, authors say in new book

We have a "Gma" health alert. New research that could help you lose weight and get healthy featured in the new book "What to eat when." It says the timing of when you eat matters just as much as what's on your plate and Adrienne Bankert has details for us. ?????? Reporter: This morning new research on the biological clock shows when you eat is as important as what you eat. In a new book about timing your nutrition, written by doctors Michael roizen an Michael krupain. To sleep better, have more energy and to just even help you lose weight. Reporter: The main goals eat when the sun is out and eat more earlier in the day and less later. It's not just about eating the right foods but eating the right foods at the right time. That's right because your circadian rhythm changes throughout the day and gets your body to eat the right thing at the right time. We want to eat breakfast and lunch your biggest and dinner should be the smallest. Reporter: When you sleep you get the benefits of intermittent fasting without being awake and hungry including weight loss, lower blood pressure and reduced cholesterol. You both were skeptics of this particular meal plan. I think when you think about shifting your meals up you think I'm going to be starving at night. But when you start eating more of your calories earlier your hunger changes so you're not as hungry as you think you're going to be. Reporter: They have tips about how to eat, no matter what life throws your way. What should you eat when you're stressed out or hangry which is a lot of times? Roasted chickpeas. It's a great krunyness to get rid of that stress and hangry. I think a lot wants is crunchy and something that will make them feel full and reach for sugar or chips. These provide that crunch. They really are crunchy. They're loaded with fiber and protein. When you are sick there are certain foods you should eat when you are not feeling well. A warm broth can help loosen up some mucus and add mushrooms, ginger an garlic. So the chicken soul shortens the duration but so do zinc lozenges. Adrienne Bankert, ABC news, New York. Dr. Jen Ashton is here. You have a degree in nutrition so tell us about the science behind this. There is a lot of science and an area of intense research. Something we've known for a long time. In the hospital we turn offer the lights at night because there's always stuff going on because there are cellular changes in our bodies that have to do with our circadian rhythms with whether it's light or dark, morning or night and that is really important. So in general when it comes to our diet and our weight, a lot of research and data supporting that we should eat more earlier in the day. So, for example, robin, you'll do the noon. A good lunchtime meal, more portion size than this. You can eat more. That isn't my lunch. But you have protein, you have vegetables and some healthy carbs. When you go to dippertime, protein and vegetables but want to leave off the carbs because if you don't burn those carbs, it's getting stored as fat. Okay, that makes more sense than if you eat earlier in the day like this you have more time to burn it off. Timing is not just about food. There are other aspect. This is what I'm telling you, literally on a day-to-day basis I'm looking through medical journals. New research supporting the effects of our circadian rhythm morning and night differences on everything from exercise performance, people do better if they work out at night, meditation, generally better in the morning, medications as we all know are dosed at various times in the day and our hormone and blood levels change hour to hour so this is real. You know there are phones that say I'm trying to do the best I can. Now have you another thing I'm supposed to do. It's challenging to change. 20% of the American workforce works at night so for them it's about making small changes, don't try to flip your day by 12 hours, make it gradually hour to hour. Experiment how it affects you. Everyone is going to be different and lastly, we live in a really high-tech world. I think we really need to respect nature. When it gets dark outside, shut it down a little bit. That's it. Okay. She has a major announcement. She's not going to make it right now but look for a major announcement. On our Facebook page and do it on Instagram. Something I hope will help a lot

This transcript has been automatically generated and may not be 100% accurate.

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